Specific rearrangements of human chromosome 3 are associated with malignancies such as small cell lung cancer, renal cell carcinoma, leukemia, and several developmental disorders. Human chromosome 21 is associated with Down Syndrome, leukemia and Alzheimer's Disease. These two chromosome contain approximately 200 million and 50 million base pairs of DNA, respectively, and therefore together potentially contain between 4,000 and 8,000 genes. Fewer than 100 genes in total have been identified, meaning that much valuable biological information is not easily accessible. In order to increase our understanding of chromosomal organization and to isolate biologically important genes, the specific aims of this proposal are to construct yeast artificial chromosome (YAC) libraries and compositional maps for chromosomes 3 and 21. The compositional maps will provide information on gene rich regions and will allow the cloning of these and other unusual chromosomal regions. The YAC libraries will be screened with unique sequences that have been placed on the pulsed field maps, and with cDNAs from various cell lines and tissues. This will result in i) rapid regional localization of YAC clones, ii) identification of additional unique sequences for pulsed field linkage, iii) generation of additional probes for the search for chromosomal translocation breakpoints, and iv) identification of expressed sequences, including some in the vicinity of translocation breakpoints. Long term objectives include: i) characterization of genes affected by the 8; 21 breakpoint seen in AML-M2, as well as those from others, ii) the development of a series of large insert clones to span large chromosomal regions, iii) the generation of well characterized YACs useful for transgenic mouse studies.